The utility of fluorosilanes, especially alkoxyfluorosilanes, as agents of CVD is widely known. For example, fluorotriethoxysilane is useful in the electronics industry for the fabrication of semiconductor devices. The fluorotriethoxysilane may be used to deposit fluoride containing silicon oxide film using a variety of techniques including plasma deposition, e.g., Homma EP 92-305 192; Spin-on-glass Homma, J. Electro. Chem. Soc., 140, 2046 (1993) and catalytic CVD Homma, J. Electro. Chem. Soc., 140, 687 (1993). The films deposited have excellent step coverage and are useful as interlayer dielectric films.
A variety of synthetic methods for the preparation of fluorosilanes are known to those skilled in the art. One general method known is the conversion of other silicon halides, in particular silicon chlorides to silicon fluorides by the action of halogen exchange fluorination agents. This can be achieved using a variety of reagents such as metal fluorides and hydrogen fluoride. Specific examples in the literature include Booth, J. Amer. Chem. Soc., 68, 2655 (1946) in which butyltrichlorosilane is converted to butyltrifluorosilane in low yield by the action of antimony trifluoride: furthermore, Marans, J. Amer. Chem. Soc., 73, 5127 (1951) demonstrates the halogen exchange converting triethylchlorosilane to triethylfluorosilane in 81% yield using 48% aqueous hydrofluoric acid.
Another general method is the substitution of a fluoride for an alkoxy or aryloxy group bonded to silicon. Examples of this approach include Marans (as above) wherein, for example, di-n-propyldiethoxysilane is converted to di-n-propyldifluorosilane in 52% yield by reaction with 48% aqueous hydrofluoric acid. Tetraethoxysilane may be converted to fluorotriethoxysilane as described by Peppard, J. Amer. Chem. Soc., 68, 76, 1946 by the reaction of antimony trifluoride catalyzed by antimony pentachloride; or, as described by Homma (as above) by the reaction of hydrogen fluoride.
The existing technologies suffer generally from low yields, the use of excess amounts of fluorinating agents or expensive reagents, and the generation of reactive by-products such as hydrogen chloride or ethanol. Thus, there continues to exist the need for a process which gives high yields of silicon fluorides from commercially available and inexpensive starting materials.